Systems and methods for sensing wear of reducing elements of a material reducing machine

ABSTRACT

The present disclosure relates generally to systems and methods for sensing wear in machines designed to reduce or break-down material. More particularly, the present disclosure relates to systems and methods for sensing wear of reducing elements used by excavation machines such as surface excavation machines. The present disclosure relates to a wear sensing system including a multi-level wear sensor protection system. The multi-level wear sensor protection system includes a first level of protection, a second level of protection, and a third level of protection.

This application is a Divisional of U.S. patent application Ser. No.15/894,314, filed on Feb. 12, 2018, which is a Divisional of U.S. patentapplication Ser. No. 14/651,951, filed Jun. 12, 2015, now U.S. Pat. No.9,890,504, which is a National Stage Patent Application ofPCT/US2013/074672, filed Dec. 12, 2013, which claims benefit of U.S.Provisional Patent Application No. 61/736,303, filed Dec. 12, 2012, andwhich applications are incorporated herein by reference. To the extentappropriate, a claim of priority is made to each of the above disclosedapplications.

TECHNICAL FIELD

The present disclosure relates generally to systems and methods forsensing wear in machines designed to reduce or break-down material. Moreparticularly, the present disclosure relates to systems and methods forsensing wear of reducing elements used by excavation machines such assurface excavation machines.

BACKGROUND

Relatively hard materials are often processed for mining andconstruction. The variety of materials include rock, concrete, asphalt,coal and a vareity of other types of earth formations. A number ofdifferent methods for reducing the size of these hard materials havebeen developed. One traditional material size reduction method has beento drill relatively small holes in the material which are then packedwith an explosive that is ignited resulting in a rapid and costeffective method of size reduction. However, there are a variety ofdisadvantages to this technique including the inherent risk of injuries,the production of undesireable noise, vibrations, and dust, and the factthat this process is difficult to utilize in situations where space islimited or where there is a potential risk of causing other gases toignite.

Due to the above-described disadvantages associated with blastingtechniques, alternative methods have been developed for reducingrelatively hard materials. The main alternative has been the use ofreducing machines having rotary reducing components that move rigid andspecialized reducing elements through paths of travel. The reducingcomponents can include rotating drums that move the reducing elementsthrough circular paths of travel. Such drums are typically attached totheir correspondng machines so that the positions and orientations ofthe drum can be controlled to bring the reducing elements into contactwith the material being reduced. Alternative reducing components caninclude boom-mounted chains that carry reducing elements. The chains aretypically driven/rotated about their corresponding booms. The reducingelements are mounted to and move along the paths of travel defined bythe chains. In use, the booms are moved (e.g., through a pivotingmotion) to positions where the reducing elements are brought intocontact with the material being reduced.

An example machine of the type described above is disclosed at U.S. Pat.No. 7,290,360. The disclosed machine is a surface excavation machineused for applications such as surface mining, demolishing roads, terrainleveling, and prepping sites for new construction or reconstruction byremoving one or more layers of material. Surface excavation machines ofthis type provide an economical alternative to blasting and hammeringand provide the advantage of generating a consistent output materialafter a single pass. This can reduce the need for primary crushers,large loaders, large haul trucks and the associated permits to transportmaterials to crushers.

The reducing elements of reducing machines have been developed towithstand the impact loads and abrasion associated with materialreduction activities. Reducing elements can be constructed in a varietyof shapes and sizes and have been labeled with various terms includingcutters, chisels, picks, teeth etc. Typical reducing elements includeleading impact points or edges and bases. The bases are constructed tofit into mouting structures that are integrated with drums or chainsused to carry the reducing elements during material reducingapplications. The harsh environment associated with material reducingapplications virtually guarantees that the reducing elements will weardown over time. Thus the reducing elements are designed to bereplaceable, while the mounting structures are not intended to bereplaced frequently. For example, when a given reducing element becomesworn, it is removed from its corresponding mounting structure andreplaced with a new, unworn reducing element.

Often, the tips or edges of the reducing elements have a harderconstruction (e.g., a solid carbide construction) than the bases of thereducing elements. When using new reducing elements to reduce material,the leading points or edges are exposed to the majority of the impactsand abrasion action. However, once the leading tips or edges becomesworn, the bases are exposed to more impacts and abrasive action. Avariety of potential problems can arise when this occurs, including thatthe bases is less efficient at breaking the material causing inefficientoperation. This inefficiency can result in generation of sparks and/orexcessive heat which can lead to a risk of explosions, as may occur in acoal mining application where methane gas can be present. Additionally,the bases will typically wear relatively quickly as compared to theleading points or tips. This is significant because the bases preventthe reducing element mouthing structures from being exposed to wear.Thus, once the leading edges or points of the reducing elements are wornaway, the machines can only be operated for a relatively short period oftime before the bases wear away resulting in a situation where themouting structures of the drums or chains are contacting the materialbeing reduced. Once a reducing elements are worn to this point, there isa risk of causing damage to the mouting structures of the drums orchains. The mounting structures are not intended to be repaired easily,so the resulting potential damage can be difficult and costly to repair.

As a result of these issues, there are significant benefits to replacingreducing elements before the wear has progressed to an unacceptablepoint. Systems have been designed to monitor the condition of cutters toallow operators to interrupt operation and replace cutters atappropriate times. Example systems for monitoring reducing element wearare disclosed in AT3826832; DE 10015005; and US 2010/0076697. Whiel wearsensing systems exist, improvements are needed in this area.

SUMMARY

Aspects of the present disclosure relate to improved methods for sensing(e.g., detecting, measuring, monitoring, tracking, etc.) the wear stateof a reducing element (i.e., a cutter, a pick, a chisel, a blade, atooth, etc.) of a material reducing machine. In one example, thematerial reducing machine is an excavation machine such as a surfaceexcavation machine used for mining, surface mining, terrain leveling,road milling, or other applications. In other examples, the materialreducing machine can include a trencher, a rock wheel, a horizontalgrinder, a tub grinder, a chipper or other type of machine that utilizesreducing elements to process a material by breaking up or otherwisereducing the size of the material.

A variety of additional aspects will be set forth in the descriptionthat follows. These aspects can relate to individual features and tocombinations of features. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive of the broad concepts uponwhich the embodiments disclosed herein are based.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a surface excavation machine incorporating areducing element wear sensing system in accordance the principles of thepresent disclosure;

FIG. 2 is a rear view of the surface excavation machine of FIG. 1showing an excavating drum and schematically showing a sensor array ofthe reducing element wear sensing system;

FIG. 3 is an end view of the excavating drum of FIG. 2 showingreplaceable breaker bars and also showing the sensors of the reducingelement wear sensing system;

FIG. 4 is a sensor layout or array for the reducing element wear sensingsystem of FIG. 3;

FIG. 5 is a perspective view of an example sensing module for a reducingelement wear sensing system in accordance with the principles of thepresent disclosure;

FIG. 6 is a plan view of the sensing module of FIG. 5;

FIG. 7 is a side view of the sensing module of FIG. 5;

FIG. 8 is a cross sectional view taken along Section 8-8 of FIG. 7;

FIG. 9 is an end view of the sensing module of FIG. 5;

FIG. 10 is a plan view of a breaker bar arrangement including twoparallel breaker bar structures for use in protecting a sensor modulearray in accordance with the principles of the present disclosure;

FIG. 11 is a profile view of one row of breaker bars of the breaker bararrangement of FIG. 10;

FIG. 12 is a perspective view showing first segments of each of thebreaker bar structures of FIG. 10;

FIG. 13 is a graph showing inductive sensor outputs at different sensingdistances for a standard target at room temperature;

FIG. 14 is a graph showing inductive sensor outputs at different sensingdistances for a standard target at different temperatures;

FIG. 15 is a graph showing sensor outputs at different sensing distancesfor a reducing element at room temperature with no lateral offset;

FIG. 16 is a graph showing sensor outputs at different sensing distancesand various lateral offsets for a reducing tooth at room temperature;

FIG. 17 is a graph comparing sensor outputs generated for a standardtarget and two different reducing element styles at various sensingdistances and also illustrating a technique for identifying the wearstatus of a reducing element;

FIG. 18 illustrates the two teeth tested in the graph of FIG. 17;

FIG. 19 illustrates a reducing element that is laterally offset from asensor;

FIG. 20 illustrates an output of the sensor with the reducing elementlaterally offset as shown in FIG. 19;

FIG. 21 shows a reducing element aligned with a sensor;

FIG. 22 shows an output from the sensor with the reducing elementaligned as shown at FIG. 21;

FIG. 23 illustrates a sensor output profile prior to filtering where theprofile includes a major output corresponding to a reducing elementaligned with the sensor and minor outputs corresponding to reducingelements offset from the sensor;

FIG. 24 is a graph illustrating the profile of FIG. 23 with the minoroutputs filtered out;

FIG. 25 shows a portion of an excavating drum having first, second andthird sets of reducing elements and also illustrates a portion of asensing system including first, second and third sets of sensorscorresponding to the first, second and third sets of reducing elements,in FIG. 25 the first set of sensors is activated so as to sense the wearstate of the first set of reducing elements and the second and thirdsets of sensors are deactivated;

FIG. 26 shows the wear state profiles of the first, second and thirdsets of sensors of FIG. 25 with only the first set of sensors activatedas shown at FIG. 25;

FIG. 27 shows the arrangement of FIG. 25 with the second set of sensorsactivated and the first and third sets of sensors deactivated;

FIG. 28 shows the wear profiles for the first, second and third sets ofsensors with only the second set of sensors activated as shown at FIG.27;

FIG. 29 shows the arrangement of FIG. 25 with the third set of sensorsactivated and the first and second sets of sensors deactivated;

FIG. 30 shows reducing element wear profiles for the first, second andthird sets of sensors with only the third set of sensors activated asshown at FIG. 29;

FIG. 31 is a side view of another surface excavation machine suitablefor utilizing a reducing element wear sensing system in accordance withthe principles of the present disclosure;

FIG. 32 is a cross sectional view showing an excavation chain utilizedby the surface excavation machine of FIG. 31;

FIG. 33 is another example of a wear sensing system showing a firstlevel of protection in the form of an initial barrier layer inaccordance with the principles of the present disclosure;

FIG. 34 shows a portion of the initial barrier layer removed;

FIG. 35 illustrates one of a plurality of sheet segments of the initialbarrier layer with fittings attached;

FIG. 36 illustrates one of the plurality of sheet segments without thefittings;

FIG. 37 illustrates the multi-level wear sensor protection system with asecond level of protection in the form of trays;

FIG. 38 is an enlarged view of a portion of the second level ofprotection shown in FIG. 37;

FIG. 39 is a perspective view of the second level of protection with anarray of trays as shown in FIG. 37;

FIG. 40 is a side perspective view of the second level of protectionshown in FIG. 37;

FIG. 41 is a cross-sectional view taken along section line 41-41 of FIG.40;

FIG. 42 is a perspective of a third level of protection in the form ofan impact absorption structure in accordance with the principles of thepresent disclosure;

FIG. 43 is a side view depicting the third level of protection;

FIG. 44 is an enlarged view of a portion of FIG. 43;

FIG. 45 is another perspective view of the multi-layer wear sensorprotection system;

FIG. 46 is an enlarged view of a portion of FIG. 45;

FIG. 47 is a side perspective view of the multi-layer wear sensorprotection system;

FIG. 48 is a cross-sectional view taken along section line 48-48 of FIG.47; and

FIG. 49 is an enlarged view of a portion of FIG. 48.

DETAILED DESCRIPTION

The present disclosure relates generally to sensing systems for sensingreducing element wear in a material reducing machine. In one example,the material reducing machine includes a rotary component such as a drumor chain that carries the reducing elements. In certain examples, thereducing element wear sensing system provides an indication of the levelof reducing element wear such that an operator can readily recognizewhen one or more of the reducing elements are in need of replacement. Incertain examples, the level of reducing element wear can be displayedgraphically or numerically to provide a qualitative indication of thespecific level of wear for each reducing element. In other examples, thesystem can provide an indication when as worn beyond a predeterminedlevel such that replacement is recommended.

Certain aspects of the present disclosure relate to reducing elementwear sensing systems that use sensors to provide general data regardingthe wear state of a given reducing element. For example, in certainexamples, sensors in accordance with the principles of the presentdisclosure provide data regarding the general wear state of a givenreducing element without determining or measuring the position of aspecific geometric point or profile of the reducing element. The sensorscan sense general physical characteristics (e.g., volume, mass, surfacearea, etc.) of the reducing elements without measuring the position of agiven point on a given reducing element. Sensors of this type can beused effectively in harsh environments such as those encountered bymaterial reducing machines (e.g., surface excavation machines,trenchers, rock wheels, horizontal grinders, tub grinders or othermaterial reduction machines). In certain examples, sensing systems inaccordance with the principles of the present disclosure can be used toassess reducing element wear of a reducing machine while the reducingmachine is conducting reducing operations. Thus, sensing systems inaccordance with the principles of the present disclosure can providereal-time wear information regarding the reducing elements of a reducingmachine while the reducing machine is being operated. In certainexamples, sensors of the sensing system are mounted in a sensingposition and need not be moved from the sensing system to a stowedposition when the reducing machine is used to reduce material. Incertain examples, reducing element wear systems used in systems inaccordance with the principles of the present disclosure can includeinductive sensors.

Other aspects of the present disclosure relate to reducing element wearsensing systems that utilize various compensation, calibration orfiltering techniques to process sensed data. In certain examples,sensing systems in accordance with the principles of the presentdisclosure can compensate for factors such as temperature and reducingelement speed. In other systems in accordance with the principles of thepresent disclosure, sensors are placed in close proximity to one anotherand also in close proximity to multiple different reducing elements. Forsuch applications, various strategies can be utilized to provide usablewear data regarding individual reducing elements. For example, filteringstrategies can be utilized to filter out data corresponding to reducingelements not intended to be sensed by a given sensor. In certainexamples, at least one sensor is provided for each reducing element. Incertain examples, at least one sensor is provided for each reducing pathdefined by one or more reducing elements of a reducing machine. Incertain examples, sensors are positioned in close proximity to oneanother and operating strategies are utilized to reduce or minimizeinterference between adjacent sensors. For example, sensors can beselectively activated and deactivated to minimize interference betweenadjacent sensors. The sensors can also be operated in sets so thatmultiple sensors can be activated at once without having adjacentsensors activated concurrently. In certain examples, a center to centerspacing of the sensors is smaller than an effective sensing distance ofthe sensors. In certain examples, a spacing between reducing paths ofthe reducing elements of the material reducing machine is smaller thanan effective sensing distance of the sensors used to sense wear of thereducing elements.

In certain examples, systems in accordance with the principles of thepresent disclosure can include structure for protecting the sensors ofthe sensing system during material reducing operations. For example,breaker bars or other blocking structures can be provided for preventingmaterial from damaging the sensors. In certain examples, the breakerbars can be positioned closer to a reducing circle or cylinder of thematerial reducing machine than the sensors. In certain examples, thesensors can also be protected by a rugged, protective housing thatcovers the sensors but does not interfere with the sensors' ability tosense the reducing elements. In certain examples, the sensors can sensethe reducing elements through the protective housings. In certainexamples, protective housings are made of a dielectric material such asplastic and the sensors are inductive sensors.

In certain examples of the present disclosure, inductive wear sensorsare used. In certain examples, the inductive wear sensors can haveoperating ranges of at least 75 mm when used with a standard target asdefined by the sensor manufacturer. In certain examples, wear systems inaccordance with the principles of the present disclosure can useinductive sensors having effective sensing distances less than 100 mm.In certain examples, the inductive sensors have effective operatingdistances greater than 50 mm.

Other aspects of the present disclosure relate to a wear sensing systemincluding a multi-level wear sensor protection system. The multi-levelwear sensor protection system includes a first level of protection, asecond level of protection, and a third level of protection. In certainexamples, the first level of protection includes an initial barrierlayer including a plurality of sheet segments made of a polycarbonatematerial. The second level of protection includes a side-by-sidearrangement of trays positioned behind the initial barrier layer. Thetrays can be configured to absorb impacts that are transmitted throughthe initial barrier layer to prevent the impacts from impacting upon thesensors. The third level of protection includes a relief structure foraccommodating impacts that are transmitted through both the initialbarrier layer and the trays. In one example, the relief structure can bepositioned behind the trays for accommodating movement of the trays inresponse to an impact that passes through the initial barrier layer andthe trays.

FIG. 1 illustrates a surface excavation machine 20 that can utilize areducing element wear sensing system in accordance with the principlesof the present disclosure. The surface excavation machine 20 includes atractor 19 having a main chassis 22 (i.e., a mainframe) including afront end 24 and a rear end 26. The main chassis 22 is supported on aground drive system (i.e., a propulsion system) that preferably includesa plurality of propulsion structures such as wheels or tracks 30 forpropelling the machine 20 over the ground. An operator cab 32 ispositioned at a top side of the main chassis 22. An excavation tool 34is mounted at the rear end 26 of the main chassis 26. The excavationtool 34 includes an excavation drum 38 that is rotatably driven (e.g.,by hydraulic motors) about a drum axis 40. The excavation drum 38carries a plurality of reducing elements 42 suitable for cutting rock.The excavation drum 38 can be mounted to a boom that can be pivotedbetween a lowered excavating position (see FIG. 1) and a raisedtransport position (not shown). A shroud 78 at least partiallysurrounds/encloses the excavation drum 38.

As shown at FIG. 2, the reducing elements 42 are depicted as teethhaving leading tips 50 supported on bases 52. In certain examples, theleading tips 50 can be harder than the bases 52. For example, leadingtips 50 can be solid, carbide inserts while the bases 52 can be hardenedsteel. In certain examples, the reducing elements 42 are removablymounted to the excavation drum 38. For example, the reducing elements 42can be fastened within mounting structures such as pockets 54 integratedwith the excavation drum 38.

In use of the surface excavation machine 20, the surface excavationmachine 20 is moved to an excavation site while the excavation tool 34is in the transport position. When it is desired to excavate at theexcavation site, the excavation tool 34 is lowered from the transportposition to the excavation position (see FIG. 1). While in theexcavation position, the excavation drum 38 is rotated in a direction 46about the axis 40 such that the excavation drum 38 uses a down-cutmotion to remove a desired thickness T of material. As the excavationmachine 20 moves in a forward direction 47, excavated material passesunder the drum 38 and is left behind the surface excavation machine 20.During the excavation process, the tracks 30 propel the surfaceexcavation machine 20 in the forward direction 47 thereby causing a toplayer of material having a thickness T to be excavated. It will beappreciated that example excavation applications for which the surfaceexcavation machine 20 can be used to include surface mining, roadmilling, terrain leveling, construction preparation and otheractivities. In other examples, the drum can be configured to excavateusing an up-cut motion.

Referring to FIG. 3, the leading tips 50 of the reducing elements 42define a reducing boundary B (e.g., reducing circle or cylinder) of theexcavation tool 34. The reducing boundary B corresponds to the generallycylindrical boundary transcribed by the leading tips 50 of the reducingelements 42 as the drum 38 is rotated about the drum axis 40. Thereducing boundary B can have a reducing diameter D. The leading tips 50of the reducing elements 42 also define reducing paths of the excavationtool 34. A reducing path is the path that the tip of a reducing elementfollows/defines when the drum is rotated. Each reducing path coincideswith a reducing path plane that is perpendicular to the drum axis 40 andthat passes through the leading tip 50 of the reducing element 42 thatdefines the reducing path. Example reducing path planes P1, P2, P3 andP4 for four different reducing paths are depicted at FIG. 2. The pathscorrespond to four different reducing elements 42. As shown at FIG. 2, asensor array 61 can be provided within the shroud 78 near the reducingboundary B. In certain examples, a reducing path can be defined by asingle reducing element 42 and a corresponding sensor of the sensorarray 61 can be aligned with the reducing path so as to be capable ofsensing the reducing element 42 when the reducing element 42 passes bythe sensor as the reducing element 42 is rotated about the reducingboundary B by the drum 38. In certain examples, each reducing path ofthe excavation tool 34 can have a corresponding separate sensor. Inother examples, two or more reducing elements 42 can be provided along agiven reducing path.

Referring to FIG. 2, the reducing path planes P1, P2, P3 and P4respectively coincide with reducing paths of reducing elements T1, T2,T3 and T4. The sensor array 61 can include separate sensors 60corresponding to each of the reducing paths. The sensors 60 can haveeffective sensing distances Y that are longer than a path spacing PSbetween the reducing path planes. The sensors 60 can be arranged inmultiple rows (e.g., three rows R1, R2 and R3) that extend along theaxis of rotation 40 of the drum. The sensors 60 can be spaced a spacingdistance Z from the reducing boundary B. The spacing distance Z is lessthan the effective sensing distance Y. The effective sensing distance Ycan be larger than the path spacing PS defined between the reducing pathplanes. The sensors 60 of adjacent rows can be staggered relative to oneanother in an orientation that extends along the axis of rotation 40. Inan example embodiment, adjacent reducing paths are not assigned tosensors in the same row. For example, as shown at FIG. 2, reducing pathplane P1 aligns with sensor S1 of the first row R1, reducing path planeP2 aligns with sensor S2 of the second row R2, reducing path plane P3aligns with sensor S3 of the third row R3 and sensor S4 aligns withsensor S4 of the first row R1. This pattern can repeat. In this way, thesensors 60 of the array can be arranged to have center-to-center sensorspacings measured along the axis of rotation 40 that match the pathspacings PS. The effective sensing distances Y of the sensors 60 can belarger than the sensor spacings SS.

In certain examples, the reducing elements 42 each have a metalconstruction and the sensors 60 are inductive sensors. In use, thesensors 60 can generate alternating electromagnetic fields through whichthe reducing elements 42 pass as the reducing elements 42 are rotatedabout the axis of rotation 40 by the drum 38. Because the reducingelements 42 each have a metallic construction, when the reducingelements 42 pass through the electromagnetic fields of the sensors 60,eddy currents form on the surface of the reducing elements 42. Theamount of energy that is transferred by this phenomenon is directlydependent upon the surface area of the reducing element 42 passingthrough the field. The amount of energy transferred from the magneticfield can be sensed by the inductive sensor and is represented by adecrease in electric current at the inductive sensor. Since the amountof energy transferred is dependent upon the size of the object passingthrough the magnetic field, the amount of current reduction sensed bythe sensor as a reducing element passes through the magnetic field isrepresentative of the size of the reducing element. As a reducingelement wears during use, the surface area of the reducing element 42passing through the magnetic field of its corresponding sensor isreduced such that less energy is transferred to the reducing element asthe reducing element passes through the magnetic field. Since lessenergy is transferred to the reducing element, a smaller reduction incurrent is sensed by the inductive sensor. Thus, by monitoring themagnitude of current reduction sensed by the sensor as the reducingelement passes through the magnetic field, it is possible to monitor thewear state of the reducing element corresponding to the sensor.

Referring to FIG. 3, the surface excavation machine 20 can include awear sensing system 70 in accordance with the principles of the presentdisclosure. The wear sensing system 70 can include a hanger arrangement72 for mounting sensor modules 74 to the surface excavation machine 20.In the depicted example, the sensor modules 74 are mounted at aninterior surface 76 of the shroud 78 that at least partially surroundsthe drum 38. The hanger arrangement 72 includes a plurality of rails 80(e.g., tracks) having lengths that extend along the drum axis 40. Therails 80 define channels 82 in which a row of sensor modules 74 arereceived. As shown at FIG. 4, the sensor modules 74 can be arranged inan array having three parallel rows of R1, R2 and R3 of sensor modules74. The rows R1, R2 and R3 correspond to channels C1, C2 and C3 definedby the rails 80 of the hanger arrangement 72. The sensor modules 74 canbe coupled (e.g., pinned or otherwise fastened) together and can beloaded into the hanger arrangement 72 by sliding the rows of sensormodules 74 longitudinally into the channels C1, C2 and C3. It will beappreciated that openings can be provided in end walls of the shroud 78for allowing the sensor modules 74 to be inserted into the channels C1,C2 and C3. During the insertion and removal process, the rows R1, R2 andR3 of sensor module 74 are slid along the channel C1, C2, C3 in anorientation that extends along the drum axis 40. When mounted in thechannels, the sensor modules 74 of adjacent rows can be staggeredrelative to one another.

The wear sensing system 70 can also include blocking structure forpreventing debris of substantial size from impacting the sensor modules74. As shown at FIG. 3, material breaking structures are attached to theinterior surface 76 of the shroud 78 at a location upstream from thesensor module 74. In certain examples, the material breaking structuresare positioned at a spacing S1 from the reducing boundary B defined bythe reducing elements 42 and the sensor modules 74 are positioned at aspacing S2 from the reducing boundary B defined by the reducing elements42. In certain examples, the spacing S2 is larger than the spacing S1.In certain examples, the spacing S2 is at least 25%, 50% or 75% largerthan the spacing S1. In certain examples, the spacing S2 is at least⅛^(th) of an inch or at least 2/8^(th) of an inch or at least ⅜^(th) ofan inch larger than the spacing S1. In certain examples, the spacing S2is about ⅝^(th) of an inch and the spacing Si is about one inch.

Referring still to FIG. 3, the breaking structure can include aplurality of breaker bar structures mounted to the interior side of theshroud 78. For example, FIG. 3 shows a breaker bar arrangement includingfirst and second breaker bar structures 84. Each of the breaker barstructures 84 has a length that extends along the drum axis 40. Thebreaker bar structures 84 each include three breaker bar sections 84A,84B and 84C that are aligned with one another to form the length of thebreaker bar structure 84. Each of the breaker bar sections 84A, 84B and84C includes a mounting bar 86 secured to the shroud 78 by reinforcinggussets 88. Each of the breaker bar sections 84A, 84B and 84C alsoincludes an impact bar 90 fastened to the mounting bar 86. The impactbars 90 are positioned the spacing Si from the reducing diameters D andare adapted to be impacted by material carried by the reducing elements42 over the top side of the drum 38 during material reducing operations.As the material is impacted by the impact bars 90, the material isreduced in size such that the material is sufficiently small so as tonot extend outwardly from the drum 38 a distance greater than thespacing S1. In this way, the material is prevented from significantlyimpacting the sensor modules 74. In certain examples, the impact bars 90are secured to the mounting bars 86 by fasteners so that the impact barscan be readily removed and replaced as the impact bars 90 wear. As shownat FIG. 3, the two breaker bar structures 84 are spaced relative to oneanother about the circumference of the drum 38 such that one of thebreaker bars structures 84 is positioned downstream of the other of thebreaker bar structures 84. In this way, material is initially impactedby the upstream breaker bar 84 and then is subsequently impacted by thedownstream breaker bar structure 84.

FIGS. 5-9 illustrate one of the sensor modules 74. The sensor module 74is configured to hold two of the sensors 60. Each of the sensors 60 caninclude a separate magnetic coil 63 (see FIG. 4). The sensor module 74includes structure for housing and protecting the magnetic coils. Forexample, the sensor module 74 includes a housing 100 including first andsecond chambers or sections 102, 104 for housing the coils 63 of theinductive sensors 60. The housing 100 is preferably made of a dielectricmaterial through which magnetic fields generated by the coils 63 of thesensors 60 can be readily transmitted. In certain examples, housing 100is made of a hard plastic material that provides impact protection tothe sensors 60 while concurrently allowing magnetic fields generated bythe sensors 60 to pass through the housing 100. As shown at FIG. 9, thehousing 100 includes flanges 106 for engaging the rails 80 of the hangerarrangement 72 to retain the sensor modules 74 within the channelsC1-C3. Electrical contacts and wiring can be provided on a back side 108of the sensor module 74 for allowing the sensor module to beelectrically connected to a control system having suitable controlcircuitry for controlling operation of the sensors 60. A metal backingplate 110 can be mounted at a back side of the housing 100. When thesensor module 74 is mounted within the hanger arrangement 72, a frontface 112 of the housing 100 is positioned the spacing S2 from thereducing boundary B defined by the reducing elements 42. The sensors 60are positioned slightly farther from the reducing boundary B than thefront face 112. For example, the coils 63 of the sensor 60 can bepositioned a distance from the reducing boundary B that is equal to thespacing S2 plus the thickness of the front wall of the housing 100. Incertain examples, the front wall of the housing has a thickness of about¼ of an inch and the sensors 60 are spaced about 1.25 inches from thereducing boundary B. It will be appreciated that in other examples,different spacings can be utilized depending upon the type of sensorused, the material being processed and the configuration of the reducingmachine.

It will be appreciated that the magnitude of the signal sensed by aninductive sensor is dependent upon the size of the target passingthrough the magnetic field of the sensor and/or the closeness of thetarget to the inductive sensor. FIG. 13 is a graph showing an outputcurve 198 of an inductive sensor at room temperature for a standardtarget. The output curve 198 of the graph of FIG. 13 shows the sensoroutput as a standard target is placed at different spacings directly infront of the sensor thereby causing the sensor to generate differentoutputs. When the standard target is outside the effective sensing rangeof the sensor, the inductive sensor output has a maximum value shown byline 200. As the standard target is moved progressively closer to theinductive sensor, the inductive sensor output gradually reduces inmagnitude.

The impedance of the coil of the inductive sensor 60 changes withtemperature. Thus, changes in temperature modify the output curve of theinductive sensor. For example, as shown at FIG. 14, the output curves ofthe inductive sensor move to the left and have steeper slopes as thetemperature decreases. As shown at FIG. 14, line 210 corresponds to atemperature of 122° F., line 212 corresponds to a temperature of 68° F.and line 214 corresponds to a temperature of 32° F. The curves 210, 212and 214 show outputs of a sensor when detecting a standard target atdifferent distances for the different temperatures mentioned above.

The difference in inductive sensor output between a worn reducingelement and a new reducing element can be small enough that temperaturevariations have a meaningful impact when assessing wear levels.Therefore, aspects of the present disclosure relate to using algorithms,look up tables or other means for compensating for temperaturevariations when monitoring reducing element wear. In certain examples,temperature sensors can be provided at the inductive sensor coils toprovide an indication of the temperatures of the inductive sensor coils.In other examples, ambient temperature or another temperature associatedwith the reducing machine can be used to approximate the temperature ofthe coils of the inductive sensors.

FIG. 15 shows an output curve 199 representing the output of aninductive sensor when sensing a reducing element at different distancesfrom the inductive sensor. For the graph of FIG. 15, the reducingelement is not offset from the inductive sensor (i.e., the coil of theinductive sensor and the reducing element are both aligned along acommon plane corresponding to a reducing path of the reducing element).The reducing element used to provide the data of the graph of FIG. 15has a smaller area than the standard target used to provide the data ofFIG. 13. Thus, the sensor output curve 199 depicted at the graph of FIG.15 has a steeper slope than the slope of the curve 198 depicted at FIG.13.

In certain examples of the present disclosure, the coils of theinductive sensors can be placed at a center-to-center spacing measuredalong the axis of rotation 40 of the drum 38 that is smaller than theeffective sensing distances of the inductive sensors and is also smallerthan the widths of the magnetic fields generated by the inductivesensors. Thus, an inductive sensor aligned with a given reducing pathcan sense a reducing element corresponding to the reducing path, butalso can sense reducing elements corresponding to adjacent reducingpaths. As shown at FIG. 16, the slope of the output curve generated bythe inductive sensor decreases as the lateral offset distance of thereducing element increases. For example, curve 300 shows the outputresponse of an inductive sensor when a standard target is positioned atdifferent distances from the inductive sensor while the standard targethas zero lateral offset from the inductive sensor. In contrast, outputcurve 302 shows the output for the inductive sensor when the same targetis positioned at the same outward distances as the output curve 300 butat a 2 inch lateral offset from the inductive sensor. The curves betweenthe output curves 300, 302 show the effect of laterally offsetting thetarget from the inductive sensor.

FIG. 17 shows three sensor output curves 304, 306 and 308. The sensoroutputs for generating the curve 304 were generated by positioning astandard target at different distances from the inductive sensor whilemaintaining zero lateral offset. The inductive sensor outputscorresponding to the curve 306 were generated by positioning a reducingelement 310 (see FIG. 18) at different distances from the inductivesensor while maintaining a lateral offset of zero. The inductive sensoroutputs corresponding to the curve 308 were generated by positioning areducing element 312 (FIG. 18) at different outward spacings from theinductive sensor while maintaining a lateral offset of zero. Since thereducing element 310 is thicker than the reducing element 312, the curve306 has a less steep slope than the curve 308. FIG. 17 also illustratesa technique for assessing reducing element wear using the output fromthe inductive sensor. For example, with respect to the tooth 310, line314 represents a baseline value for the tooth 310 when the tooth is new.This baseline value can be stored in memory of a control system (e.g., acomputer, a processor, or other electronic device) and used to controloperation of the wear sensing system. Line 316 is representative of anoutput of the inductive sensor when the tooth 310 becomes worn. In oneexample, the tooth 310 wears about ½ an inch between the line 314 andthe line 316. In use, when the output value generated by the inductivesensor reaches the line 316, the operator can be notified that thecorresponding tooth 310 should be replaced. Line 318 corresponds to anoutput from the inductive sensor when the reducing element 312 is new.Line 320 corresponds to an output from the inductive sensor when thereducing element 312 has worn to a state where the reducing element 312should be replaced. Once again, a controller of the reducing elementwear sensing system can monitor the outputs of the inductive sensorcorresponding to the tooth 312 and can alert an operator that the tooth312 should be replaced once the output of the inductive sensor reachesthe line 320. As indicated above, the outputs of the inductive sensorcan be modified by algorithms, look up tables or other means tocompensate for factors such as temperature and speed. In this regard, itis noted that the speed at which the reducing element is traveling whenthe reducing element passes through the alternating magnetic field ofthe inductive sensor can also affect the output of the sensor. Forexample, as the rotational speed of the drum is increased withoutchanges an outward spacing between the inductive sensor and the reducingelement being sensed, the change in current sensed by the sensor as thereducing element passes through the magnetic field is reduced. Toovercome this factor, an algorithm can be used to modify the output ofthe inductive sensor to compensate for the rotational speed of the drum.

FIG. 21 shows a reducing element 42 interfering with the magnetic fieldof a sensor 60 and therefore being detected by the sensor 60. Thereducing element 42 is shown at an outward spacing distance d1 and alateral spacing distance of zero. FIG. 22 shows an output of theinductive sensor with the reducing element at the position of FIG. 21.FIG. 19 shows the reducing element 42 laterally offset from the sensor60 by a lateral spacing distance d2. The reducing element 42 is alsooffset from the inductive sensor 60 by the outward spacing distance d2.The outward spacing distance d1 is the same at FIGS. 19 and 21. FIG. 20shows an output of the inductive sensor 60 with the reducing element 42in the position of FIG. 19. A comparison of FIGS. 20 and 22 shows thatan output signal 401 generated by the sensor 60 when the reducingelement 42 is directly in line with the inductive sensor 60 has a largervariance as compared to a non-sensing reading 401 of the sensor 60 thana corresponding output signal 402 generated by the inductive sensor 60when the reducing element 400 is positioned at the same outward spacingdistance d1 but also at a lateral spacing distance d2. The graph of FIG.20 also demonstrates that inductive sensors 60 are capable of sensingreducing elements that are laterally offset from the sensors but stillwithin the magnetic field of the sensor.

As shown at FIGS. 19 and 20, reducing elements that are laterally offsetfrom a given inductive sensor 60 can be detected by the inductive sensor60 as the reducing elements move past the sensor 60. In certain examplesof the present disclosure, the cutting paths defined by the reducingelements 42 can be sufficiently close together that one of the inductivesensors 60 can detect the reducing elements corresponding to three ormore of the reducing paths. For example, FIG. 23 shows an initial,unfiltered sensor output profile for the inductive sensor 60 for onerotation of the drum 38. As the drum 38 rotates, the inductive sensor 60senses the reducing element 42 that is aligned with the inductive sensor60. The sensor 60 also senses the reducing element 42 corresponding tothe reducing path that is offset to the left of the inductive sensor 60and the reducing element 42 that corresponds to the reducing path offsetto the right of the sensor 60. Because the left and right reducingelements are laterally offset from the sensor 60, signal readings 450Band 450C corresponding to such reducing elements have a smaller variancein magnitude as compared to a reading 450A corresponding to the alignedreducing element. As indicated at FIG. 23, rotational positions Ω_(a),Ω_(b) and Ω_(c) of the center, left and right reducing elements aredetermined and saved in memory. During a filtering process, themagnitudes of the readings 450A, 450B and 450C are compared and thereading 450A with the greatest variance from zero is selected. Therotational position Ω_(a) of the highest reading 450A is saved inmemory. The readings 450B and 450C can then be filtered out as shown atFIG. 24. Thereafter, the control system will only look for inductivesensor reading values corresponding to the aligned reducing element atthe rotational position Ω_(a). If the system does not detect a reducingelement at the rotational position Ω_(a), then the operator can benotified that the aligned reducing element is missing. As the reducingelement wears, the magnitude of the signal reading 450A at rotationalposition Ω_(a) will change. A certain magnitude of change of the signalreading 450A as compared to a base-line signal reading value (e.g., thereading when the reducing element was new) is indicative of the reducingelement being worn to a point where the reducing element 42A should bereplaced. At this point, the operator can be notified that the reducingelement 42A should be changed.

In certain examples, the inductive sensors 60 are positionedsufficiently close to one another that the magnetic fields of adjacentsensors 60 overlap one another. Thus, if all the sensors 60 wereoperated simultaneously, the magnetic fields of adjacent sensors couldinterfere with one another. To prevent this type of magneticinterference, in certain examples, all of the sensors 60 are notoperated at the same time. For example, in one example, each of thesensors 60 can be individually operated such that readings areindividually taken with respect to each of the reducing paths. In suchan example, the controller can use a control protocol that repeatedlycycles through the sensors with each sensor being individually actuatedfor at least one rotation of the drum 38. In other embodiments, steps orgroups of the sensors 60 can be simultaneously actuated and the controlsystem can cycle through the groups of sensors 60. In certain examples,the sensors of each group can be selected based on the relativepositioning of the sensors and the positioning of their correspondingmagnetic fields. Specifically, the sensors of any given set are selectedso that the magnetic fields of the sensors within the set do notinterfere with one another.

FIGS. 25-30 relate to a system having multiple sets of sensors 60 thatare sequentially energized in de-energized. As shown at FIGS. 25, 27,and 29, only a portion of the length and the circumference of the drum38 are depicted in a laid-flat view. For example, only about 90° of thecircumference of the drum is depicted and only ¼ of the length of thedrum is depicted. The depicted portion of the drum includes reducingelements A1, B1, C1, A2, B2, C2, A3, B3, and C3. The sensing systemincludes a first set of sensors A, a second set of sensors B and a thirdset of sensors C that all interface with a controller 500. Thecontroller 500 controls the operational speed of the drum 38 via ahydraulic motor 502 and a gear box 504. The controller also controlsoperation of the inductive sensor sets A, B and C. For example, during afirst sensing phase, the inductive sensors corresponding to set A areactivated and the inductive sensors corresponding to sets B and C aredeactivated. With the sensors of set A activated and the sensors of setsB and C deactivated, near readings are taken for the reducing elementsA1, A2 and A3 as shown at FIG. 26 and no readings are taken for thereducing elements corresponding to sets B and C. As shown at FIG. 26,specific reading values (e.g., input 1 from inductive sensors) androtational positions (input 4) for each of the reducing elements A1, A2and A3 are identified by the controller. During the first phase ofsensing, the sensors of set A sense the wear level of the reducingelements A1, A2 and A3 as the drum rotates through one or morerotations.

After the first phase of sensing, the controller implements a secondphase of sensing in which sensor sets A and C are de-energized, andsensor set B is energized (FIG. 27). The controller takes wear readings(e.g., input 2 from the inductive sensors of set B) for reducingelements B1, B2 and B3 as shown at FIG. 28. The input 2 valuescorrespond to the wear levels of reducing elements B1, B2 and B3. Thecontroller can have pre-saved information relating to the rotationalpositions of the reducing elements B1, B2 and B3. Additionally, thecontroller can compare sensed wear level values generated by the sensorset B corresponding to each of the reducing elements B1, B2 and B3 andcan compare such values to base level wear values of the reducingelements B1, B2 and B3. The base level wear values can correspond tovalues established when the reducing elements B1, B2 and B3 wereinitially installed on the drum 38. In comparing the sensed wear levelvalues generated by the sensor set B for each of the reducing elementsB1, B2 and B3 to their corresponding baseline wear levels, thecontroller can use algorithms or other means to compensate forvariations associated with temperature, the rotational speed of the drumor other factors. Once wear readings for the reducing elements for B1,B2 and B3 have been established, the controller can stop the secondphase of sensing and move to a third phase of sensing.

FIG. 29 shows the system in a third phase of sensing. In the third phaseof sensing, the sensor sets A and B are de-energized, and the sensor setC is energized. With the sensor set C energized, the controller canaccess input 3 values from the sensors of set C relating to the wearlevels of the reducing elements C1, C2 and C3 (see FIG. 30). Typically,the wear level values are generated by the sensor set C as the drum isrotated. The sensed wear level values of the reducing elements C1, C2and C3 can be compared to base-line wear level values for the reducingelements C1, C2 and C3. The base-line wear level values for the reducingelements C1, C2 and C3 can be established by the system when thereducing elements C1, C2 and C3 are initially installed on the drum 38.If the sensed wear level values indicated by input 3 deviate from thebase-line wear level values by a predetermined amount, the system canindicate that replacement of one or more of the reducing elements C1, C2and C3 is recommended or required.

It will be appreciated that certain readings taken by inductive sensorsin accordance with the principles of the present disclosure are generalin nature and do not identify the position of a specific geometric pointon any of the reducing elements. Instead, the readings taken by thesensors provide a general indication of the overall surface area of agiven reducing element that passes through the magnetic field of thesensor corresponding to the reducing element. The reading can varydepending upon the size and shape of the reducing element. In thisregard, different wear patterns on the reducing element can yieldsimilar readings. For example, similar yield readings may be yielded ifportions of the base wear away while the tip remains intact or if thetip is removed and the base remains fully intact. Advantageously,sensing systems in accordance with the principles of the presentdisclosure provide a good indication of general wear while concurrentlynot using precise optical technology that is not compatible with useduring normal operation of the reducing machine. Thus, sensing systemsin accordance with the principles of the present disclosure can be usedwhile their corresponding material reducing machines are being used toreduce materials and do not require material reduction operations to bestopped to allow for wear sensing. Additionally, sensing configurationsin accordance with the principles of the present disclosure have ruggedconstructions that can remain in a sensing position during materialreduction operations and are not required to be moved to a stowedposition during material reduction operations.

In practice of aspects of the present disclosure, a reducing element isinitially installed on a drum or chain. The drum and/or chain is thenrotated and a base-line wear reading is taken with respect to theinstalled reducing element. The base-line wear reading can be takenusing a sensor such as an inductive sensor. At the time the base-linewear reading is taken, a temperature value (e.g., a temperaturerepresentative of the coil temperature) and a rotational speed of thedrum or chain are identified. The base-line wear reading as well as thetemperature value and the rotational speed value can be saved in memory.The machine can then be operated to perform material reductionoperations. While performing material reduction operations, a real-timewear reading can be taken with respect to the reducing element using thesensor. Real-time temperature and rotational speed readings can also betaken. Once the real-time readings have been taken, the real-time wearreading and the base-line wear reading can be compared to assess a wearlevel of the reducing element and to determine whether the reducingelement has worn to the point where the reducing element is recommendedor required to be replaced. In comparing the real-time wear reading tothe base-line wear reading, the controller can make adjustments to thereal-time wear level value and/or the base-line wear level value tocompensate for any differences that may exist between the base-linetemperature value and the real-time temperature value and/or between thebase-line rotational speed and the real-time rotation speed. If thebase-line and real-time wear readings differ by a predetermined amountafter compensation, the controller can provide an indication to anoperator that replacement of the reducing element is recommended orrequired.

At initial installation of the reducing element, the controller candetermine a rotational position of the reducing element and filter outreadings corresponding to reducing elements not desired to be sensed forthe particular sensing operation being performed. When the controllertakes the real-time wear reading, the controller looks for a readingfrom the sensor at the pre-identified rotational position of the chainor drum that corresponds to the reducing element in question. If noreading is detected at the pre-identified rotational position, thecontroller recognizes that the reducing element is missing and providesan indication to the operator that the reducing element is missing andrepair or replacement is needed.

FIGS. 31 and 32 show another surface excavation machine 720 suitable forusing a reducing element wear sensing system of a type described herein.As compared to utilizing a drum, the surface excavation machine 720includes reducing elements 742 carried by a chain 738. The chain 738 isdriven by a gear 739. By monitoring the speed and rotation of the gear,and by knowing the circumferential length of the chain 738, it ispossible to monitor the rotational position of the chain 738 during use.In certain examples, the rotational position of the chain can beidentified by sensing reducing elements arranged in a non-repeatingconfiguration along a given reducing path. A non-repeating configurationis a configuration that does not repeat over the course of one fullrotation of the chain. The simplest non-repeating configuration is asingle reducing element corresponding to one sensor and/or one reducingpath. By detecting the presence of the single reducing element andmonitoring the speed and rotation of the chain 738, the controller canestablish a position of the reducing element on the chain and candetermine the rotational position of all the other reducing elements onthe chain. Another example of a non-repeating pattern includes tworeducing elements monitored on the same reducing path that are notuniformly spaced about the perimeter of the chain.

FIGS. 33 and 34 show another example of a wear sensing system 800 inaccordance with the principles of the present disclosure. The wearsensing system 800 can include a multi-level wear sensor protectionsystem 802. The wear sensor protection system 802 is configured toprotect wear sensors 804 (see FIG. 34) from damage under the mostextreme conditions. The multi-level wear sensor protection system 802 isalso configured to allow the wear sensors 804 to provide sensingfunctionality during milling operations. Thus, the wear sensing system800 can provide continuous tooth wear monitoring without requiringinterruptions in milling operations for assessing tooth wear. Themulti-level wear sensor protection system 802 includes a first level ofprotection, a second level of protection, and a third level ofprotection. The first level of protection is illustrated and describedin more detail in FIG. 35.

The first level of protection can be in the form of an initial barrierlayer 806 (e.g., initial shield layer). In one example, the initialbarrier layer 806 surrounds the reducing drum (not shown) and ispositioned between the reducing drum and the wear sensors 804. In oneexample, the initial barrier layer 806 curves at least partially aroundthe reducing drum. In one example, the initial barrier layer 806 canhave a radius of curvature centered on the axis of rotation of thereducing drum. In certain examples, the initial barrier layer 806 canhave a sheet-like construction including a plurality of sheet segments808 secured to the machine frame 810 in a side-by-side arrangement. Incertain examples, the initial barrier layer 806 can include a materialsuch as polycarbonate. In FIG. 34, the initial barrier layer 806 isshown with portions of the plurality of sheet segments 808 removed.

Referring to FIGS. 35-36, one of the plurality of sheet segments 808 isdepicted. In the depicted example, the sheet segment 808 includes a mainsegment body 812 having an upper end 814 and a lower end 816. In certainexamples, the upper and lower ends 814, 816 of the main segment body 812can respectively be secured with upper and lower fittings 818, 820(e.g., fixtures). The upper fitting 818 can include fastener openings822 for receiving fasteners (not shown) used to secure the sheet segment808 to the machine frame 810 (see FIG. 33). The lower fittings 820 caneach include a first tab 826 and a second tab 828 that fit withincorresponding tab receptacles 830 (see FIG. 34).

In certain examples, the plurality of sheet segments 808 can includeopenings 807 (see FIG. 36) at the upper and lower ends 814, 816 of themain segment body 812. The plurality of sheet segments 808 can besecured to the fittings 818, 820 using fastening bands 809 that includeapertures (not shown) that align or correspond with the openings 807 ofthe plurality of sheet segments 808. In one example, the fastening bands809 are attached to the plurality of sheet segments 808 using fasteners811 (e.g., rivets, cap screw, pins, ties, adhesive, etc.) to secure theplurality of sheet segments 808 to the upper and lower fittings 818, 820respectively.

The initial barrier layer 806 can have a robust construction. In certainexamples, the initial barrier layer 806 can be easily replaced and has arelatively low cost. In certain examples, each of the plurality of sheetsegments 808 can be installed by sliding the sheet-like structuredownwardly about the rotor along a guide track until the first andsecond tabs 826, 828 fit within the corresponding tab receptacles 830secured to the machine frame 810. Thereafter, fasteners can be used tosecure the upper ends 814 of the plurality of sheet segments 808 to themachine frame 810.

In certain examples, the upper ends 814 of the plurality of sheetsegments 808 are at a location that is easily accessed by an operator.To remove one of the plurality of sheet segments 808 for replacement,the fasteners at the upper ends 814 of each of the plurality of sheetsegments 808 are removed and the plurality of sheet segments 808 areslid upwardly to disengage the first and second tabs 826, 828 from thetab receptacles 830 and to slide the plurality of sheet segments 808 outfrom around the reducing component.

Referring to FIG. 37, the multi-level wear sensor protection system 802can also include a second level of protection in the form of trays 832(e.g., housings) 832 in which the wear sensors 804 are mounted. Incertain examples, the trays 832 are mounted behind the initial barrierlayer 806 and are configured to absorb impacts that are transmittedthrough the initial barrier layer 806 to prevent the impacts fromimpacting upon the wear sensors 804 contained within the trays 832. Incertain examples, the trays 832 include a wear resistant material suchas polycarbonate. The trays 832 help provide impact protection to thewear sensors 804 while concurrently allowing magnetic fields generatedby the wear sensors 804 to pass through the trays 832. The second levelof protection is illustrated and described in more detail in FIGS.38-42.

Referring to FIGS. 38-39, details of the trays 832 are illustrated. Thetrays 832 can be configured to hold the wear sensors 804 such that thewear sensors 804 are open- faced within in the trays 832 (i.e., thetrays do not cover the major outer faces of the sensors). FIG. 38 is anenlarged view of a portion of the second level of protection shown inFIG. 37. In the depicted example, several trays 832 are shown in aside-by-side arrangement. In one example, the trays 832 can be mountedtogether along a plate 834. The plate 834 can be arranged and configuredto slide a plurality of the trays 832 and wear sensors 804 as a unitinto channels 836. As depicted, the channels 836 are constructed to beparallel to one another.

In certain examples, rails 838 can be attached to the plates 834. Therails 838 can have lengths that extend along the drum axis. The rails838 can be secured (e.g., welded, coupled) to the plate 834 opposite tothat of the trays 832. The plate 834 can be slid longitudinally into thechannels 836 that extend along the drum axis.

Referring to FIG. 39, an array of trays 832 is depicted along the plate834. The plate is shown attached to the rails 838. In certain examples,the plate 834 can be inserted in channels 836 from a right side of themachine. It will be appreciated that the plate 834 including the arrayof trays 832 can also be inserted into channels 836 from a left side ofthe machine.

Referring to FIG. 40, a side view of the array of trays 832 positionedalong the plate 834 is shown. FIG. 41 shows a cross-sectional view ofthe array of trays 832 shown in FIG. 40.

Referring to FIG. 41, the third level of protection is depicted. Thethird level of protection includes an impact absorption structure 840(e.g., relief structure) for accommodating impacts that are transmittedthrough both the initial barrier layer 806 (see FIG. 37) and the trays832. In the depicted example, electrical contacts and wiring 842 areshown on a back side of the wear sensor 804 (see FIG. 39) for allowingthe wear sensor 804 to be electrically connected to a control systemhaving suitable control circuitry for controlling operation of the wearsensor 804. A metal plate 844 can be mounted to the impact absorptionstructure 840 adjacent to a back side of the wear sensor 804. The impactabsorption structure 840 is illustrated and described in more detail inFIG. 42.

Referring to FIG. 42, an example of the impact absorption structure 840is illustrated. The impact absorption structure 840 includes a base 846that can be attached to the plate 834 (see FIG. 41). The base 846 candefine a plurality of apertures 848 for receiving fasteners (not shown)to couple the impact absorption structure 840 to the plate 834. Incertain examples, the base 846 of the impact absorption structure 840can define a center opening 850. The center opening 850 can beconfigured to receive a grommet 852 (see FIG. 41). In certain examples,the impact absorption structure 840 can be arranged and configured tobend and flex about legs 854 upon impact.

Referring to FIG. 43, a side perspective view of the third level ofprotection is shown. FIG. 44 is an enlarged view of a portion of FIG.43. In FIG. 44, the impact absorption structure 840 (e.g., reliefstructure) can be positioned behind the trays 832 to help accommodatemovement of the trays 832 in response to an impact that passes throughthe initial barrier layer 806 (see FIG. 37) and upon the trays 832. Thelegs 854 of the impact absorption structure 840 are configured to bendupon impact.

In some examples, the impact absorption structure 840 can include astructure that in-elastically deforms in response to an impact. In suchsituations, the impact absorption structure 840 will remain bent uponimpact. It will be appreciated that such structures would likely requirefixing or replacement more often than a resilient structure. In otherexamples, the impact absorption structure 840 can be made of a plasticmaterial for providing flexibility upon impact such that the impactabsorption structure 840 does not remain bent upon impact.

In certain examples, the impact absorption structure 840 can include anelastic/resilient structure that biases the trays 832 toward a sensingposition and allows the trays 832 to move away from a reducing componentin response to an impact. After impact, such resilient impact absorptionstructures 840 can bias the impacted trays 832 back toward theircorresponding sensing positions. The third level of protection isillustrated and described in more detail in FIGS. 44-48.

Referring still to FIG. 44, the legs 854 of the impact absorptionstructure 840 can be coupled to the trays 832 to secure the trays 832along the plate 834. The plate 834 having the impact absorptionstructure 840 mounted thereon is shown positioned within the channel836.

Referring to FIG. 45, a bottom view of the multi-layer wear sensorprotection system 802 is shown. Details of the construction of themulti-layer wear sensor protection system is illustrated and describedin more detail in FIG. 46.

In FIG. 46, an enlarged view of a portion of FIG. 45 is shown. Theconstruction of the multi-level wear sensor protection system 802 allowsfor a unit of trays 832 secured to the impact absorption structure 840to be inserted into the channels 836 from either a left or right side ofthe machine by the plate 834.

Referring again to FIGS. 44 and 46, the plate 834 can slide into thechannels 836 on top of ledges 856. In certain examples, the ledges 856can be welded to elongated members 858 that extend longitudinally alongthe drum axis. In one example, the rails 838 (see FIG. 40) locatedwithin the channels 836 can receive wedges 860.

Referring to FIG. 47, a side view of the multi-layer wear sensorprotection system 802 is shown. FIG. 48 is a cross-sectional view of themulti-layer wear sensor protection system 802 illustrating the array oftrays 832 in the channel 836 along the drum axis. FIG. 49 is an enlargedview of a portion of FIG. 48.

Referring to FIG. 49, the wedges 860 can include a tapered end 862. Inone example, the wedges 860 can be inserted along the rails 838 (seeFIG. 46) from the left and/or right sides of the machine. Thus, therails 838 can guide the wedges 860 during insertion. The wedges 860 canbe inserted such that the tapered end 862 of the wedges 860 engage aramp surface 864 in a center portion of the channel 836 when fullyinserted.

In one example, the wedges 860 provide downward force to the plate 834to clamp down on the trays 832 to provide stability and keep the plate834 in place. For example, the plates 834 are clamped against the ledges856. In certain examples, the wedges 860 can be coupled to L-shapedbrackets 866 to keep the wedges 860 in position. In one example, thewedges 860 can be bolted to the L-shaped brackets 866. The L-shapedbracket 866 can be attached to the main bracket 868 (see FIG. 47) andcan be moved relative to the main frame via fasteners to control theposition of the outer ends (i.e., the non-tapered ends) of the wedges860 to ensure the plate 834 is firmly clamped against theledges/shoulders 856 of the channels 836 along its entire length.

From the forgoing detailed description, it will be evident thatmodifications and variations can be made without departing from thespirit and scope of the disclosure.

What is claimed is:
 1. A wear sensing system comprising: a multi-levelwear sensor protection system, the multi-level wear sensor protectionsystem including a first level of protection, a second level ofprotection, and a third level of protection; wherein the first level ofprotection includes an initial barrier layer, the initial barrier layercomprising a plurality of sheet segments; wherein the second level ofprotection includes a side-by-side arrangement of trays positionedbehind the initial barrier layer, the trays are configured to absorbimpacts that are transmitted through the initial barrier layer toprevent the impacts from impacting upon the sensors; and wherein thethird level of protection includes a relief structure for accommodatingimpacts that are transmitted through both the initial barrier layer andthe trays, the relief structure is positioned behind the trays foraccommodating movement of the trays in response to an impact that passesthrough the initial barrier layer and the trays.
 2. The wear sensingsystem of claim 1, wherein the relief structure includes a structurethat in-elastically deforms in response to an impact.
 3. The wearsensing system of claim 1, wherein the relief structure includes anelastic structure that biases the trays towards a sensing position andallows the trays to move away from a reducing component in response tothe impact.
 4. The material reducing machine of claim 1, wherein thetrays hold inductive sensors and each tray has an open front face thatdoes not cover a major face of its corresponding sensor.